10 36/50: Installation and Operation Manual
Level Control
A maximum gain reduction of 60dB can be achieved with a control voltage of +10V; the rate
of attenuation is approximately 165mV per dB. A control voltage of zero realises unity gain
(full volume), however, with no external connection to pin 2, an internal 4k7 resistor
connected to the +15V power will ‘pull up’ the control voltage to provide maximum
attenuation. The output impedance of the control voltage source should be low enough to
overcome the influence of this resistor.
Source Select
Line 1 +7.5V
Line 2 +6.0V
Line 4 +3.0V
Line 5 +1.5V
Line 6 0V
With no external connection to pin 3, an internal 15k resistor connected to +15V will ‘pull up’
the source select control voltage and the ‘off’ position will be selected. The output impedance
of the control voltage source should be low enough to overcome the influence of this resistor.
If you would like to fix the music signal to a particular line input, wire a fixed resistor from the
table below between pins 1 & 3 on the remote control connector:
Line 1 16k
Line 2 11k
Line 3 6k8
Line 5 1k8
Line 6 shorting link
If the control voltage source is not isolated from the power earth, there is a small risk of
creating a ‘ground loop’ by linking the mixer technical ground (0V) to the ground (0V) of the
equipment providing the control voltages. To minimise the risk, we suggest that all pieces of
equipment be positioned in close proximity and supplied from the same power outlet.
25 Solving problems
25.1 Ground loops (aka Earth loops)
Here are the details of the music source select control voltages (pin 3) required to switch the
six line input signals:
Off >+9.0V
Line 3 +4.5V
Line 4 3k9
Despite your best efforts, if the completed sound system ‘hums’ you probably have a ‘ground
loop’; the offending signal source can be found by setting the volume control to minimum
then disconnecting the input leads (both left & right channels) on each line input until the
‘hum’ disappears. This problem is often caused by terminating a screened input cable into a
signal source positioned a significant distance from the mixer. A good way of avoiding this
potential problem is to use signal sources (CD players and the like) that are double insulated
with no connection to the mains supply earth. If a signal feed were derived from a second
mixer (a club or microphone mixer for example) it would be perfectly normal to expect this to
be earthed; we suggest that a transformer be used to isolate the signal and prevent a noisy
loop (See diagram on following page).
25.2 Connecting balanced signals to the unbalanced line inputs.
We recommend the use of a transformer to convert a balanced signal to an unbalanced
signal suitable for direct connection to the mixer line inputs. The transformer should be
mounted close to the Zone Mixer and the unbalanced output lead should be kept as short as
possible. Where both the source unit and destination mixer are earthed, it is important to
isolate the primary and secondary windings to avoid a potential ground loop; if there is any
doubt about this, we suggest that the balanced cable screen is not connected at the
transformer end. Suitable transformers for this application are the RS Components 210-6447
06/12/02 V5.0
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